1. Field of the Invention
This invention relates to a method for fabricating planar micro-bridges and SQUIDs.
2. Description of the Prior Art
Methods used in the prior art to fabricate submicron-wide lines, such as electron beam and X-ray lithography, are generally limited to practical dimensions of about 0.2 to 0.3 microns (1 micron=10.sup.-6 meters). These techniques are costly and difficult to implement. If atoms are evaporated at angles to thin film edges, submicron features can be defined with dimensions of 0.2 micron or less, and this only requires the use of conventional optical masks to define the thin-film edges.
Previous shadowing techniques are tedious to use, however, and are often difficult to control. These prior art methods are described in detail in U.S. Pat. No. 3,898,353, to L. S. Napoli et al., entitled SELF ALIGNED DRAIN AND GATE FIELD EFFECT TRANSISTOR, which issued on Aug. 5, 1975; another description of this prior art method appears in the Applied Physics Letters, January 1979, under the title "A Simple Method for Fabricating Lines of 0.15 Micron With Using Optical Lithography".
A disadvantage with prior art methods is that some require etching subsequent to the shadow deposition, thus, (a) degrading the correlation between opposite sides of the shadow regions, (b) requiring etching out a cavity underneath the submicron shadow region, which is extremely hard to control and observe, and (c) requiring the use of an etch-resistant material for the shadowing deposition, thus making it very difficult to remove later. The invention hereindescribed addresses these prior art problems with a new shadowing technique.